A major problem in the operation of motor vehicle air conditioning systems is that moisture in the form of water vapor is picked-up during operation of the system by migration of water vapor through tubing or seal devices into the refrigerant flowing through the system. In time such moisture can adversely affect the operative components of the system. Several solutions have been proposed in which a separate can type unit is filled with desiccant which removes moisture from the refrigerant as it circulates through the system.
One type of motor vehicle air conditioning system has an engine driven compressor connected to the vehicle engine by a belt pulley drive which includes a cycling clutch controlled to turn the compressor on and off to regulate the refrigerant supply in accordance with the cooling demand. The system has an accumulator on the low pressure refrigerant vapor side of the system. The accumulator is located downstream of the evaporator and includes a chamber filled with desiccant to dehydrate the refrigerant passing through the system.
Another approach to dehydration of refrigerant flow in a motor vehicle air conditioning system is used in systems in which the compressor is driven continuously and the refrigerant flow is controlled by a control valve located between the condenser and the evaporator and responsive to temperature conditions in the system. In such systems a receiver filled with desiccant is located in the high pressure fluid side of the system, usually downstream of the condenser and upstream of the control valve. In cases where there is an inadequate reserve charge of refrigerant, vapor can enter the thermal expansion valve causing a detectable high pitch "hiss" noise as the vapor expands across a valve orifice. The receiver separates vapor from liquid and provides a column of liquid to a thermal expansion control valve. This column of liquid is essential for proper functioning of the flow control valve. In the past, the receiver was located downstream of the condenser. In order to achieve subcooling of the liquid refrigerant, it was necessary to have a sufficient refrigerant charge to fill the receiver with liquid refrigerant which would then back up into the subcooling passes for further cooling.
In such cases, a reserve charge of refrigerant is required. In order to reduce the quantity of reserve charge, the present invention either eliminates or changes the locating of a standard receiver/dehydrator for supplying liquid to the thermal expansion valve.